It’s not the first time I’ve gone a bit nutty over my dog. I’ve rearranged vacations for him, bought insanely expensive organic kibble and have taken him to private indoor swimming lessons. To me, Gus is more than a dog; he’s my baby.

Am I crazy?

I might be, but then so are a lot of people — especially if the thesis of new book called “What’s a Dog For?” (original title “Dogs are Not Humans”) is to be believed.

The book’s author, New York magazine editor John Homans, wanted to avoid what befell me when he first adopted Stella, a black Lab mix. But over time, what initially was concrete — “dogs are not humans!” — became something more mutable.

“Who, or what, is she?” he writes in his first chapter. “What goes on in her head? And what’s going on in my head that I can’t help but treat her as something she clearly isn’t?”

The result of such ponderings is this book, a fascinating tour through ever-changing perceptions of dogs as pets.

There were 77 million dogs in the United States in 2010 (up from 53 million in 1996). Nearly 100% of their owners speak to them like humans and over 80% view them as family members. One survey revealed that 14% of coupled dog owners would chose Fido over their significant others. Another, quoted in the book, revealed that a shocking number of dog owners would save their pet in a life-threatening situation over a fellow human.

President Obama once spoke about an “empathy deficit” after Hurricane Katrina — but there was no such deficit in the outpouring of funds and attention devoted to saving the storm’s abandoned pets. Animal rescuers even marked houses for pets the same way the National Guard did for humans.

“People are living more isolated lives, are having fewer children, their marriages aren’t lasting,” British professor James Serpell is quoted in the book. “What’s happening is simply that we’re allowing animals to fill gaps in our lives.”

Loneliness only amplifies the wish to anthropomorphize pets. And dogs have actually evolved to take advantage of this very innate drive. The “infant schema” of a dog’s face (the high forehead, big eyes, floppy ears, for examples) might prod our innate response to want to nurture.

“Stella hypnotizes me with her big brown eyes, making me forget her gleaming wolfish teeth and the notion that, as I’ve been told, she’s a parasite. She plays me like a violin. It’s irresistible — she’s really a marvel of design,” Homan writes.

Perhaps we’ve gone too far treating dogs like surrogate children at the expense of other humans — especially since the science of canine emotion and intelligence is still largely inconclusive.

Though dogs outperform chimps and small children in pointing tasks, which caused some scientists to call dogs communicative “mind readers,” some researchers pooh-pooh the results as “a basic simple form of learning,” much like what a rat or pigeon would do.

Other studies hypothesize that dogs have gotten dumber as they’ve evolved and haven’t needed to hunt to survive.

Smart or dim, dogs are still an increasingly focal part of our household as they never were before. They are in our beds, at our jobs and on our vacations. Some of our medicine cabinets are even stocked with fancy doggy pharmaceuticals for the sad, bored or anxious pup. This is happening even as the science studying humanization of dogs is still largely inconclusive.

Behaviors like jealousy, pride, envy, guilt and shame are believed to separate us from the animal kingdom. But ask any dog owner, and she’ll swear her pup is capable of all the above; ask any scientist and the answers are less certain. Labs at Duke, Harvard and Columbia (to name only a few) have devoted many research projects to answering these very questions.

Fairness, for example, was tested by giving one dog a treat for giving a paw while as second one is ignored. The study found that the dog that was ignored was less likely to do the trick again. Jealous? Envy? A sense of moral injustice? It sounds promising, but the results were deemed “inconclusive.”

Another study in 2009 examined the famous “guilty look.” In it, owners ordered their dogs not to eat a treat left behind but were fooled into believing that their dogs had disobeyed when they hadn’t. When owners scolded their angelic pets, they behaved in ways associated with guilt — head downcast, ears drooping, etc. The study concluded that the “guilty look” was largely anthropomorphic, a product of the scolding, not a result of guilt itself.

The problem with dog cognition research is that “people want to believe it,” scientist Ray Coppinger tells Homans. “They want to give dogs somethings special. And no one has ever come close to showing that they’re different from any other mammal.”

Dogs likely not have gotten smarter or more emotionally complex — but then again most humans haven’t, either.

I, for one, just re-upped my doggy swim-class membership and bought a doggy Burberry raincoat (for any future storms), and, like a dog, I feel no shame about it.